Antistatic device



May 5, 1942. H. MOURADIAN ANTISTATIC DEVICE Filed Jan. 22, 1940 4 Sheets-Sheet l CARRIER 1 F'i mm -'Bl 3 TO QC.

SOURCE BAND PASS FILTER BAND PASS FILTER LINE 0R TELEPHONE STATION ,TO D.C. GEN. .OR RECT.

F I G. I

CARRIER T0 D.C. SOURCE 'BIAS H GH PASS FILTER Fl G.

INVENTOR.

May 5, 1942 H. MOURADIAN ANTISTATIC DEVICE Filed Jan. 22, 1940 4 Sheets-Sheet 2 H 1s 15 In] G B'AND PASS FILTER i P I I4 is I 17 BAND l H V PASS 1" 3 1 FILTER T0 uc. TOINTERM 2 TO o.c. SOURCE FRE .osc.(p SOURCE Flt-3.3

T0 AUDIO LOW AMPL. To PASS AND SOURCE FILTER LOUD v SPEAKER T0 0.c. T0 osc. T0 c. SOURCE SOURCE FIG 4 IN VEN TOR.

y 5, 1942- l H. MOUIRADIIAN' -2;282,299

ANTI-STATIC DEVICE Filed Jan. 22, 1940 4 Sheets-Sheet 3 CARRIER -su\s MTOD.C.

. SOURCE D'" 7 i A 1 BAND. :1 I PASS FILTER T 1 3 TOTELEPHONE TOD.C.GEN- um: 0R STATION 0R RECT.

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INVENTOR.

T0 OSCILLATOR g f g'i ll L y 5, 1942- H. MOURADIAN I 2,282,299

ANTISTATIG DEVICE Filed Jan. 22, 1940 4 Sheets-Sheet 4 TOOSCILLATOTTZ TOD.C. T3

L2 2 17 Kg T0 M Auolg L3 EQUIPT. 19

IN VEN TOR.

Patented May 1942 UNITED STATES PATENT OFFICE 2,282,299 ANTISTATIC DEVICE Hughes Mouradian, Philadelphia, Pa. Application January 22, 1940, Serial No. 314,960 23 Claims. (01. 25o 1o) This invention relates to a radio transmission and receiving system and, more particularly, to the specific arrangements at both transmitting and receiving stations for the purpose of eliminating or reducing to a very low minimum static effects, as well as internally produced disturbances at the receiving station or stations.

There have lately been described in the art several effective methods of reducing static disturbances. types, using different instrumentalities for obtaining the desired results:

1. The use of multiple receiving antennas with volume and phase adjusting means for adding the signal impulses received and reducing the static impulses.

2. The use of a wide band of frequencies, in conjunction with frequency modulation, instead of amplitude modulation. Such a system has been described in a comprehensive manner by Prof. Armstrong in a paper published in I. R. E. Proceedings, May 1936, pages 689- 3. The use of two separate carrier frequencies for transmitting and receiving, each carrier frequency modulated in accordance with present practice and each including therefore, an upper and a lower side band, with the intensities of the two carriers themselves so phased as one of them to be at its maximum while the other is at its minimum. At the receiving end, the phases of the two carriers are again reversed.

The present disclosure differs from both of the above general methods described in subparagraphs 1 and 2, in that no multiple interconnected receiving sets are required, nor is it necessary to use a wide band of frequencies to obtain the desired efiect. As well known, and as fully described by Armstrong, the use of a wide band of frequencies entails the use of very high frequency carrier, 40-150 megacycles, and precludes the utilization of the present day broadcasting range of frequencies. The frequency band required, with the high frequency carrier, is of the order of 200,000 cycles. This may be compared with the usual broadcasting band of 10,000 cycles to obtain an idea of the relative dimensional factors involved.

The method first disclosed in these specifications also differs from the arrangements described in sub-paragraph 3 in that special means are used to effectively suppress either the lower or the upper side band using, to effect this pur- These have been of several differentside band transmission,

pose, double modulation at the transmitting end in conjunction with electric filters and is further carrier-suppressed throughout. Several variations have been disclosed at the transmitting end. In one variation single frequency carrier is used, in contrast with the double frequency method referred to in sub-paragraph 3. In a second variation where a double frequency transmitting system is used, both carriers are again suppressed thus enabling the use of adjacent carrier frequencies. This last feature further distinguishes the carrier-suppressed, single side band double frequency system of the present specifications from the arrangements previously disclosed by prior inventors. In all such prior arrangements, all using double frequency double a separation of the order of at least 15,000 cycles was required between the two fundamental frequencies of the double frequency system to avoid the carrier interference effect, or whistle.

A third variation which is also first disclosed in these specifications and is superimposed upon the first two variations consists in the chopping of the signal spectrum itself into a number of adjacent pairs of frequencies. Each pair still being of the single side band type and also carrier suppressed. We thus have, in this third variation, a multi-frequency transmitting system which, as clearly and definitely proved in these specifications, has the advantage of still greater ranges in static interference reduction. All of these several transmitting systems have their corresponding counterparts in the various receiving systems designed to operate in cooperative relation with the transmitting systems disclosed.

The reduction of static interference and also of internal noise has been, as well known, a prime preoccupation of the radio engineer. Except in the field of frequency modulation the improvements obtained in static reduction have been comparatively small even with multiple receiving antenna systems, i. e. of the order of 6-9 db., where the frequencies involved are in the broadcasting or low frequency range. Probable reduc'- tions in static of the order of 40 decibels and over have been shown as effectively obtainable in the attached specifications with the arrangements herein disclosed.

It is necessary in order to get a birds eye view of the problems involved and of the importance of the novel solutions first disclosed in these specifications to bear in mind several well-established facts. First, that the total interference effect is directly proportional to the total width V times as large.

-mind is that in all systems which depend for indicates of the band of frequencies allowed to enter the receiving equipment. For instance, where in order to receive both side bands, as in the systems broadly referred in sub-paragraph 3, the receiving equipment must be designed to receive a band twice as large, the noise power is four The second point to be borne in their functional operation upon two interference waves mutually reacting against each other the effectiveness of the reaction depends upon the frequency separation between the two interference waves.

S=Separation in frequency between the two carriers of the double frequency system.

In the case of the present system, as first disclosed in'these specifications, the corresponding frequency separation is just 8, instead of (ZS-I-S) as in the case of systemspreviously disclosed. In view of the general considerations briefly outlined hereinabove, which affect the primary purpose of the invention, a second most'important advantage of the systems first disclosed in these specifications will be immediately apparent, i. e., the number of usable radio signalling channels will be several times greater with the systems herein disclosed than with similar systems heretofore disclosed. No changes in the number of radio signalling channels allocated by the Federal Communications Commission would be required, if all radio channels made use of'the systems herein disclosed. A substantial reduction in the number of such radio channels of communication in use today would, on the contrary, have to be made if the similar'systems,,such 'as' those described in. sub-paragraph 3.were to be generally adopted.

A third, equally as great'an 'advantaga f some of the receiving systems disclosed in these specifications consists in the possibility of using these systems for receiving directly'the broadcasts frompresent day single frequency carrier, double side band broadcasting stations, without loss of the fundamental characteristic of static reduction. This is not possible with the systems described insular-paragraph 3 hereinabove.

view of its importance, this point is reviewed in great detail with the description of the operational characteristics of the receiving system of I Figure 3 and Figure 4 of the drawings. This invention will'be clearly understood from I the following description, when read in connection with the attached drawings, of which'Fig. l and Fig. 2' show the conventional typebroadcasting equipment adapted for double carrier In the casev of the The relative effectiveness is in- Y versely proportional to the separation in absolute- No detail explanations are required for an understanding of the operation of the conventional type radio broadcasting equipment which terminates in terminals 1, 8 of Fig. 1 of the drawings. The essentially novel features of the arrangement consist in the use of two-step modulation for the purpose of separating the two side bands produced by modulation. The first step in the modulation is carried out at a sufficiently low frequency to enable this separation effectively and conveniently. The second step in the modulation, which is illustrated on Fig. 2 of the drawings, merely steps up the frequency to the frequency assigned for normal operation to the broadcasting station or point-to-point transmitting station. It will be noted that an essentially new feature of the arrangement consists in the 'use of carriers C1 and C2, the frequency of carrier C1 being cycles per second. The numerical values of pi and m are chosen so that r is equal to the band width of the speech or signal spectrum which it is desired to transmit. Thus, if the transmission of speech frequencies within the band 100 to 10,000 cycles (for the upper limit) is desired, then 5 27F -l0,00(l cycles Thechoice of pi and 132 for the frequency factors of the respective carriers is made-so that effective separation of the lower side bands can be made by means of filters from the upper side bands. At

- the present stage of the development of the art,

and double modulation as required by the invention; Fig. 3 and Fig. 4 show the conventional type receiving equipment adapted for double carrier jand double demodulation; Fig. 5 indicates a variation of Fig. 1 of the drawings, which uses a single side band transmission; Fig. 6 indicates a variation of Fig. 3 of the drawings. 'Fig. 7 indicates a, variation of Fig; 4 'of the drawings; Fig; 8 static disturbance neutralizing equipment to care for residual unbalances of equipment impedances and residual variations of intensity of staticWith absolute frequency.

such effective separation can be conveniently made, at frequencies as high as 80,000 cycles per second requiring, however, the use of crystal filters for the purpose. Band pass filterA of Fig. l of the drawings allows the free transmission of frequencies included between 72 and (f2+10,000) cycles, thus suppressing the lower side band. Correspondingly, bandpass'filter B allows the free transmission of frequencies .between (f1+l0,000) and f1 cycles, again eliminating the lower side band. The upper sideband emerging from terminals l, 2 will be proportional to kCS cos{(p2 +q)t+0} and the corresponding upper side band emerging from terminals 5, 6 will beproportional tolcCS cos {(p1+q)t+0} wheremk coefficient of proportionality C=common amplitude of carriers C1 and C2 l9= C Omm011 phase'angles of carriers C1 and C2 :ainplitude of signal I An important feature of the invention isv the To recapitulate, the important points involved are the use of the u per side bandsonly and the reversal in phase of one ofthe side bands. 'Evidently equivalent results would be obtained, as will be seen later, if a transposition had been cut in between terminals 5, 6 and I, 8 instead of between I, 2 and 3,4. It will also be evident that instead of the two upper side bands of carriers 01 and C2, the two lower side bands could have been chosen, withthe complete exclusion of these upper side bands.

Attention is here called to the fact that the total width of the frequency spectrum utilized is no greater, with the arrangement shown on Fig. 1 and Fig. 2 of the drawings than with the pres-. ent day arrangements of double side band broadcasting. Furthermore, nothing in this invention restricts the total band width to twice 10,000 cycles. It could be anything desired for ordinary broadcasting purposes and it could be, s'ay, 2,000,000 cycles wide if broadcasting television impulses. The descriptions given .in'the specifications and the arrangement of the drawings have been restricted, for purposes of convenience, to conventional broadcasting-or point-to-point speech communication circuits.

Terminals 1, 8 of Fig. 2 of the drawings connect to terminals 1, 8 of Fig. 1 of the drawings. The purpose of the arrangement shown on Fig. 2 of the drawings is to step up the frequencies of the two side bands by f cycles to the normal frequency (f2+,fo) assigned to the broadcasting station. This is carried out through the use of amplifier C (optional), followed by the second modulator D, with carrier C3 supplying current at frequency in. Since the wave expressed by Equation 1 has two terms, the second modulating step produces four main waves (omitting from consideration the higher harmonics which are eliminated by low-pass filter E2). We can, if we so choose, select again the upper side bands of the second modulator D. This is carried out by means of the high pass filterEh of the drawings, which allows the free transmission of all frequencies above (f1+fo) cycles and virtually eliminates all frequencies below 1+fo) cycles. The equation of the wave radiated by the transmitting antenna of Fig. 2 of the drawings is given by Formula 2, below. 1

It will be noted that the transmitting system above described is carriersuppressed throughout, since the radiated wave as givenv byFormula 2 does not contain the carrier itself, but only two (upper) side bands. The suppression of the intermediate carrier is obtained on Figure 1 of the drawings by the symmetrical feed of the carrier supply through the midpoint of a choke coil in the input circuit of the modulator, and the mid-point of the output transformer of the modulator.

The suppression of the final carrier of frequency (f1+fo) is obtained by the action of the high pass filter E, which allows only the flow of currents exceeding (f1+fo) cycles in frequency. In any transmittingsystem which operates on a double carrier basis, it is impossible, of course, to avoid the beat note or whistle between the carriers, unless these two are separated in frequency by 15,000 or 20,000 cycles so as to render said beat note inaudible. In the absence of a system suppressing the carrier, therefore, the frequency spectrum used by any double frequency transmitter would include twice the side band frequency plus the 15,000 cycles or so required to avoid the beat note. If the radio transmission system is restricted by regulation to a 5 kilocycle width for each side band, then the frequency spectrum required would be 25,000 cycles wide. In the case of the transmitting system described in the specification and as shown on Fig. 1 and Fig. 2 of the drawings, where this system is applied for regular radio broadcasting purposes, the frequency spectrum required is only 10,000 cycles wide. This is due to the fact that only the upper side bands are allowed through (by the action of filters A and B of Fig. 1 of the drawings) and these being adjacent in frequency, the entire width of the spectrum required is twice the side band width of 5 kilocycles or just 10 kilocycles wide. This is of tremendous practical importance, since should the broadcasting companies see fit to make the changes required by Fig. 1 and Fig. 2 of the drawings, it would be possible to operate all present day broadcasting stations without mutual interference, but with greatly reduced static. The transmitting system described in the present specifications results therefore in maximum economy in the use of the ether.

Figure 3 and Figure 4 taken together show the arrangement required at the receiving end. The equipment shown on Fig. 3 of the drawings includes, in addition to the receiving antenna, the usual radio-frequency amplifier F and the intermediate frequency modulator G, followed by' band pass filters H and J. Evidently, except where point-to-point transmission is involved, the modulator G must be supplied with means for varying the frequency in of the intermediate carrier. After demodulation, the resultant waves are passed through filters H and J, which select the lower side bands in each case. The main waves involved have the frequency factors (pz-i-q), (p1+q), (2pu+pz+q). The band pass filter H is designed for a free transmission band included between the frequencies of f2 and '(f2+10,000) cycles, while band pass filter J is designed for the band f1 and (f1+10,000) cycles. As stated hereinabove, the free transmission band width of 10,000 cycles may be anything determined upon in advance. The wave reaching terminals l3, I4 will be given by- The wave reaching terminals [1, 18 will be given by- Z=coefiicient of proportionality C4=amplitudeof carrier supplied to demodulator G 62=phase difference We may note, now, that a transposition has been inserted in the upper side band between terminals l3, l4 and [5, I6. The result of this transposition is to change the sign of this upper side band so that this side band wave, when it reaches terminals l5, I6 has the expression- C at a fixedfrequency f1. Thefinal resultof the demodulation process illustrated on Fig. 4 of the drawings is a speech wave which is given by the expression- Z'=coefficien t of proportionality C=common amplitude ofcarriers of frequency f1 and f2 supplied to demodulators L and We will now consider what effect the arrangement shown on Fig. 3 and Fig. 4 of the drawings has upon the static disturbances collected by the receiving antenna or produced by the receiving equipment (thermal agitation in antenna circuit, the grid circuit of the radio frequency amplifier, shot efiects, etc., in all partsof the receiving circuit preceding band pass filters H and J) We will designate the amplitude of a single disturbing sinusoidal wave in the frequency range (fo+f2+ 10,000) by Na and the corresponding amplitude of a single disturbing wave in the frequency range (fo+f1+10,000) by Nb. The corresponding phase differences will be indicated by pa) and ((pb). The actual frequencies of the two disturbances Na and Nb will be designated by (fo+f2+fn) and (fo+f1+fn) With the above assumptions, the total disturbance will therefore be designated by the summations The values of fn will vary only between O'and 10,000 (or whatever band width other than 10,000 cycles might have been preselected for the band of useful signals), since all frequencies outside this range are eliminated by the filters included in the radio receiving circuit of Fig.3 and Fig. 4 of the drawings. Considering the disturbance waves in pairs, as already suggested,

the frequencies of these two waves are stepped down by it cycles through the action of the demodulator G, and their respective amplitudes and phases become m=coefiicient of proportionality C4=amplitude of carrier C4 of frequency f (a) mNaC4 cos {(pz+p1r.)t+goa} (b) V +mNbC4. cos {(Zh-l-ZhDt-I-(pb'l After transmission through elements K1, L1

and the low pass filter M of Fig. 4 of the drawings, the expressions for waves a and b will become (b) wherem'=coeflicient of proportionality C=common amplitude of carriers supplied to demodulators L1 and L2.

The total disturbance in the loud speaking equipment will then be expressed by- The summation signs include all frequencies in between 0 and 10,000 cycles.

It will be clear by inspection of the expression for the noise, as given by Formula 4, that the disturbing effect of such noise has now two terms which are in opposition of phase, instead of being directly additive as they are with present day arrangements where both side bands, the so-called upper and lower sides of a single modulation step, are transmitted. Incidentally, the two-side band transmission of Fig. 1, Fig. '2,

Fig. 3 and Fig. 4 of the drawings should not be confused with the double side band transmission of the present art. The important difference, outside of the physical separation of the side bands required by the present invention, is that the phase differences of the twin side bands of the present art are of opposite sign, i. e.,+0 and 0, while they are of the same sign in the present invention. This point is extremely critical in the final elimination of noise from the useful speech or signal impulses.

If the "noise disturbances, as usually assumed in present day practice, include frequencies in the whole spectrum (fo-f-f2+10,000) and (fo+f1) and are substantially uniform in amplitude N and phase difference (p, then Summation 4 is given:

m'C4C'{(Nb cos (pb"Na cos M} cos pat- (Nb sin golW-Na sin goa") sin put Suppose we designate- (6) Nb sin (pb"Na. sin 1pc" by N sin X (7) Nb cos b"Na cos (pa' by N cos X Bearing in mind (6) and (7), we can rewrit Equation 4 in the more compact form:

(8) Static disturbance=mNC40'2 cos (pnt-l-X) where The total noise power, as so called and as given by (mCMCWZN cos (pnt+X) is thus thesummation of all terms similar to N for all frequencies included in-the band 0 to 10,000

,5.'7%; hence a total change of 7%.

cycles per second, Where the phase difference (wb-) is substantially equal to zero, the noise power for frequency in is practically equal irm-Na I A drastic reduction in noise power and, in favorable cases, an actual obliteration of noise, is the result of the arrangement first described in these specifications.

The following discussion will give a closer insight into the meaning and limitations of Equation 8 for noise disturbance. A

It may be noted that while Nb or Na and 45b" or 'a" are extremely variable, their differences are not random but are closely interrelated. Static disturbances, as well known, are duejxto electric discharges taking place at more or less distant points, each such disturbance being best represented by recurring very short period impulses. Where, for instance, a short period impulse has a square'wave form, it can be represented by a Fourier series consisting of a fundamental and an infinite array of harmonics. The amplitudes N of these harmonics are, as well known, inversely proportional to their frequencies. The part of this impulse spectrum that is received on a radio receiver is a small band of the very high order of harmonics. Since the frequency difference between the highest and lowest frequencies'is small compared to the midfrequency of the band, all of the frequencies received are of practically equal amplitude N. These harmonics are, furthermore, so related to each other by virtue of their relation to a common fundamental frequency that they are all in phase at the instant the impulse starts'or stops. Since the source of the static, however, is usually atquite some distance there will be, inaddition to the small variations with frequency'of noise intensity N, additional variations brought about by the variation with frequency of the attenuation of the waves between the point where the impulse originated and the receiving station. For instance, if the source of disturbance is at a distance of 500 kilometers from the, receiving stations, the difference in intensity of the received ground waves (for 1 k.w. radiated power) for 500 kilocycles and 1000 kilocycles is as follows:

Microvolts per meter 500 kilocycles 20 1000 kilocycles 0.9

(See International Radio Consulting Committee Report on Radio Wave Propagation, I. R. E. Proceedings, Oct. 1938, page 1196, Fig. 2.) By interpolation we find, for the corresponding intensity at 750 kilocycles, microvolts per meter and, for a -kilocycle frequency change from 750 kilocycles, a change of 5.7%. Now, as to the probable variation at the source, as above stated, the relative variation would be, for the same 10 kilocycle change of frequency, around a 750 kilocycle carrier:

Intensity change 10 10 kllocycles 0013 The above two variations are cumulative since the intensity of the higher harmonic is smaller by 1.3% and the relative attenuation greater by It will be noted that, for'the sky waves,.no distinction as to variation in intensitywith frequency is being of the International Radio Consulting Committee made (see page 1198, Fig. 4, I. R. E. Proceedings). It would seem proper to conclude, in view of the fact that static disturbances will utilize sky transmission as well as ground transmission, that the variation in intensity for a change in frequency of 10 kilocycles will be less than 7%. If, instead of 500 kilometers, we had assumed that the source of static disturbance was 1000 kilometers, or even a greater distance away from the receiving station, then the ground wave would be negligiblysmall, the sky wave would be definitely dominating an'd, as shown above, no material change in amplitude is noted for sky waves in the radio art today for all frequencies designated as medium frequencies in the Report (C. C. I. R.) referred to hereinabove. It is therefore not unreasonableto assume that if we take 10% as the possible maximum difference in in'- tensity between frequencies 10 kilocycles apart at any given instant of time, for a broadcasting or transmitting carrier frequency, due to a single source of disturbance, we will not be too far from the truth. 'In factgthe figure just indicated is really a high maximum when considering the receiving conditions for the present day broad casting range'of frequencies. 'In this case, if the source of "static is located 500 miles from the receiving station, the sky wave will dominate over the direct transmission wave by a ratio of 50 to 1. Since for the sky wa've'no change in attenuation need be expected (see Fig. 5, Committee Report on Wave Propagation, page 1199, I. R. E. Proceedings, October, 1938) we need not consider any difference in amplitude between frequencies 10,000 cycles apart due to this cause. The source of static has to be not more than -125 miles before diiferences of attenuation factors need actually be considered. For a distance as short as this, as just indicated, the percentage change in attenuation for a difference of 10,000 cycles will be about" 2.5% around750 kilocycles and the'total change 3.8%. This last figure means that the improvement shown in Formula 11 can 'be'exceeded by 6 db. As'to the effect of distance upon phase'differences, such phase difference between two different harmonics 10 kilocycles apart, would be brought about, if the velocity of transmission of two radio 'waves 10 kilocycles apart in frequency,would be substantiallydifferent. None apparently has been noted inthe art.. If there had'been any appreciable diiference, such difference would have resulted in'the distortion of speech waves. None, at least so 'far, has been noted. In view of the facts just noted, the relative noise power with the arrangement'herein first described, as compared with the corresponding noise power with present-day double side transmission is given by the ratio--' (N;,N,,) (0.9.l.0,) .01

, (N;,+N,,)? (0.9+.1.0) ?m The'abov'iratio means a reduction in noise power expressed in decibels equal to (11,),

log m 361=10X2.57=25-.7 db.

the resulting disturbance waves would still be given by Formulas 4 to9 inclusive, with the exception that thesign of thephase difference of zand radiating the other.

the component N is now p"5 instead Of-l-fip'fb,

assuming Nb is of the lower side band type and" N9. is of the upper side band type. Equation 9,

r Even if we had theideal situationwhich, with the arrangement of the present specifications,

results in N=0 as already shown,we wouldob tain for the single carrier double sideband arrangement with one'side band reversed of Formula 9a, a probable average given by the-lawof random variations. 7

' V N (average)=2NZj% The law of random variations'is applied here sincethe phase (p" of of the disturbancewave is absolutely uncontrollable and will. have ran,-

dom values distributed between 0 and 21r and cos (qm'L-I-gqb") will take values varying between 0 andil.

' The fundamental importance of the use'of two carriers with two retained side bands offthe sametype (after elimination of the opposite side bands) isthus made evident as a'static, as well as internal disturbance, eliminating device." It

. is therefore broadly claimed as a fundamental conception. The. transmitting arrangement, as shownzon Fig. 1 and Fig. 2 of the drawings, uses two' side bands (both upper or lower) with twomodulatingcarriers. This arrangement utilizes thesame frequency spectrum as the present day double Itis not strictly necessary, however, for the purposes of the present side band arrangements.

invention, to use two side bands'at the transmitting station. The use of a single side band would be sufficient, thus realizing economies in equipment. costs and making it possible to. use additional transmitting or broadcasting station call assignments bythe Federal Communications Commission. Such an arrangement is described on'Fig. 5 of the drawings. same system as shown on Fig. 1 of the drawings,

It is essentially the except that modulation is carried out at a single carrier frequency, instead of two different frequencies separated by the width of the. signal spectrum as in Fig. 1. It will be recalled that the receiving equipment uses, for the second step of modulation, the two carrier frequencies hand f2, which latter frequency exceeds f1 by the width of the signal spectrum. The carrier frequency of Fig. 5 of the drawings can be either f1 0r f2. In what follows, it is assumed that the carrier frequency of the first modulator, i. e.,'the modulator associated with Fig. 5 of thedrawings, if f2 7 cycles. Where the final radiated carrier frequencyis quite low, as it is for instance with the long wave- Transatlantic telephone circuits, the

two steps in the modulation process can 'be' merged into a single step, with resulting" greater economies in installation. In general, however, 7

the two step modulation process is indicated in vention..

' l4 and I5, l6 of Fig.3 of'the drawings.

The wave given by Formula '12 is amplified by the intermediate amplifier (optional, depending upon the amount of amplification'required) and:

is next stepped up in frequency by modulator D by In cycles. main products of modulation is allowed to get through by high pass filter E1 and the expression of the wave radiatedby the transmitting,

antenna is given by 7 (13) rows cos {(pz+po +q)t+0 Q No changes will be required withv the above described single side bandsystem, in the receivingequipment of Fig.a3-and Fig. 4 of the drawings. .If, now, the demodulating process is carried at frequency in, the resulting-side band wave which is allowed to pass by filterH, will be given by- (14) 1603048v cos {(p-2,+q)t+02} All of the useful speech frequencies are, in

this case, included in the band f2 and (f2+10,000)

cycles. Hencathere will be nospeech currents flowing through filter'J. "After further amplification by element K1 of Fig. 4 and a second demodulation by element L1, the final speech spec- V trum reaching the loud speaker will be given by- (15) l'cc5c4c's cos iqr+e3 The negative sign has' been used in view of the phase reversal introduced between terminals [3,

sign reversal is of no practical significance since we are dealing with a single speech wave and all components are aiiected alike.

Since no changes were introduced in the ar rangement of Fig.3 and Fig. 4 of the drawings, the reception of static and certain other internal disturbances will remainiexactly as previously described. Hence, the amplitude of these disturbances is still given bythe t'woequivalent summations, Formulas 4 and 8.

It will be noted that with the system just described, the ratio of signal power to noise power is only or 6 db. less, than with the arrangement'using 7 two side bands shown on Fig. 1 andFig. 2 of the drawings. This willbe clearly evidentby comparing Formulas l4 and 3.

In view of the-large investment already in? curred in the broadcasting and transmitting stations which are designed to operate on the familiar double side band arrangement of the present art, the question arises whether the receiving system first described in these specifications can be used to advantage in conjunction with these stations. {r l r 'There appears to be no way of using both side bands of the double side band arrangement of the present art and still retain the static disturbance reduction feature of the present in- I find, however, that'it is possible to block off one side band and use the other in the manner described below and still obtain the same advantage'sas can be secured by the use of Fig. 5

Only the upper side band of the This tenna is given, for the standard double side band arrangement of today, by-

(16) C cos pt+kCS cos {(p+q) t+} kCS cos {(1 1) 13-0} where p=frequency factor of carrier C C=amplitude of carrier radiated by transmitting antenna.

The resulting demodulated wave is given by- C4 cos {(p-p1)t01'}-carrier supplied by element G.

The first term and the second term are passed freely by band pass filter J, which has the cutoff frequencies f1 and (f1+10,000) cycles per second.

The third term, which represents the image of the side band wave given by the second term of Formula 18 is blocked off completely since it includes components which individually have frequencies lower than the lower cutoff point of filter J and, obviously, also lower than the lower cutoff point of filter H.

The speech wave which reaches the loud speaking equipment, after amplification by element K2 and demodulation by element L2, is given by- The first term in Wave 18, after the second demodulation by element L2, results in a direct current component and remains in the plate current of the demodulator L2.

The reception, amplification, demodulation, etc., of static and internal noise disturbances follow exactly the same path and pattern as heretofore described. The signal to noise ratio is therefore the same as indicated for the single side band transmitting system of Fig. and Fig. 2 of the "drawings in conjunction with the receiving system of Fig. 3 and Fig. 4.

There is a second setting of the intermediate frequency oscillator which can the blocking out procedure provided, further, additional equipment to that shown on Fig. 3 and Fig. 4 of the drawings is supplied. The equipment referred to would consist of a third demodulator and a second low pass filter admitting frequencies between 0 and 10,000 cycles, which would be wired between element M and the audio amplifier equipment of Fig. 4 of the drawings. This third demodulator would be supplied by carrier C5 at a frequency of 10,000 cycles. The sec.- ond setting is that given by the equationment G, is given by-- be used, still by v The first and third terms will be passed freely by band pass filter H. The second term is blocked out since all its components have free quencies which are higher than the higher cutthe oscillator associated 1 small variation with frequency eliminated by said filter.

off point of filter H and, obviously, also higher than the higher cutoff point of filter J.

The wave passed by filter H--after.amplification and demodulation by elements K1 and L1, respectively, is given by--- 1 X W cycles per second the resultant is given by- (23) Z"CC4CC5S cos (qt+60s'). where l =coefficient of proportionality The first term of Equation 22, when demodulated, results in a direct current component, which remains in the plate circuit of the third demodulator. l It remains to be show that the static disturbance reduction feature has'notbeen adversely affected.

The noise component, as given by Formula 8, when modified by theaction of the third demodulator,,will be given by- I (24) Noise:

The first term in the above equation, including 0 to cycles The second term merely transposes or inverts a noise component of 22% cycles into a noise component of (W-m) cycles at the same equivalent amplitude, so far as it is relative to the amplitude of the speech waves. This transposition is immaterial, for the reasons that have been fully'described in conjunction with the analysis of the relatively and phase of static disturbances within the band of frequencies received by'Fig. 3 and Fig. 4 of the drawings.

The second setting of the oscillator of demodulator G, as given byEquation 20, does result in a system enjoying the benefits of static reduction,

but it suffers under the handicap of requiring an additional demodulator and filter, with no ting advantages as compared with the first setting which is given by Equation 17. For this reason the electrical equipment arrangement for utilizing this second setting, in the manner described hereinabove, has not been illustrated on the drawings.

Thetwo settings, as given respectively by Equations'l'l and-20, have the frequencies (F-f1) and (F-f2'10,000) where F is the frequency of the of the amplitude offset- I dent that the wave leavin filter 'A will'be given by I: of filters A and It should be remem-,

L1 and L2 results in inverting one of these side bands (the lower frequencyside band). It is impracticable, as previously'noted, to use both side bands of thedouble side'band system of the present art in view of the points just mentioned. Summarizing the preceding analysis, it may be stated that there is just a single settingof the frequency of the variable frequency oscillator of Fig.

3 of the drawings, which allows for the reception -berecl that f, as before, represents the width of the signal or 'spee'chi spectrum which it is desired to transmit. There will beno'changerequired'in Fig. 2 of the drawings. The wave radiated by the transmitting antenna is given-by 27) lcC'C3S cos {(p2+po+q)t+0i} +k'CCsS co s {(p1+p0+q)t+01} At the receivingend, the arrangement required is shown on Fig; Sand Fig. 7 of the drawings, which replace Fig. 3 and Fig. l, respectively. The ree vea waveis amplified '37 radio frequency amplifier Fahd stepped down in frequency by de modulator The output of which are connected four band pass filters-H1,

' H2, J1 and J2, with the following cutoif points:

of one side band of the 'double'side band system of the present art with resultant radical improvement in static disturbance reduction. While a great many different methods for obtaining this setting will be apparent to those versed in the art,

perhapsthe simplest operating method for the receiving set of Fig. 3 and Fig, 4 of the drawings,

' when used in conjunction with transmitting stations utilizing the double side band transmission of thepresent art, is to open the'circuit at demodulator L1 and vary the "setting of the oscillator of demodulator G until the distant transmitting station is properly tuned in. When this setting has been obtained, in. the simple manner justdescribed, the circuit interruption at demodu latO T Li maythen be restored and the full advantages of static disturbancereduction obtained.

Where it is necessary to obtain a greater reduction than that given by Formula 11 I find that such further reduction can be securedby using the following modifications in the transmitting and receiving arrangements previously described.

The equipment arrangement at the transmitting station will still be given by Fig. 1 and Fig. 2 of the drawings, but the design of the apparatus will followsomewhat difierent lines. Carrier C1 will be adjusted, as before; to deliver current at a fref is the width in cycles of the speech or signal spectrum. Filters A and B will be designed as 1 follows:

' Outofi fre- V quencies Lower Higher new... f1 n+1 i .Filter. A L f f +3f With these adjustments in mind, itwill be evi- (35. V QIThewave leaving band filter B will be given 1 2 I +kcs cos {(p1+q )'t- |-0} I Y Itlw ill be noted that the fundamental difference between thedouble side band arrangement I previously described and thepresent one is that I the frequencies of the two carriers 01 and C2 are now'separa'ted by 2], or twice the free pass band 7 Q quency of f1 cycles, but carrier 02 will now be re- 'quired to deliver current at (h-j-Zf) cycles, where g terminals 3, 4 of band i There will evidently be no signal currents flowing through band pass filtCI'S'Hl and J1, in view of the effect of filters A and B at the transmitting end. There will, however, be static disturbance and internal noise currents flowing through these band pass filters just mentioned, as well as through filters H2 and J2. Y

Considering first the efiect upon the received signals of the circuit shown on Fig. 6, it may be noted that the output current of demodulator G isgiven by- 1 i I (28) ZC'C'3C'4SV 00s {(p2+q) t+02} The signal current expressed by the first term in Equation 23 will r n w through band pass n1- ter Hz, the second term flowing through filter J2. The first current amplified by element K2 and demodulated by element L2 of Fig. 7 of thedraw- V ings, will reach terminals 23, '24 and its amplitude willbegivenby (29) l'cc3c';c';s cos (qt-F03) The current expressed by the second term of Formula '28 after amplification" by element K4 and *demodulation. by element L4, will reach terminals 21, 28 with an amplitude given by-* (30 iz'ocgoic's ,cos t pe) Inview of the tra sposition T3 introduced bethe final-signal tween terminals 23, and 25, .26, current reaching the audio or other low frequency signal equipment will be given by This is enactly the same equation as given by Formula 3. Thus the arrangement indicated on Fig. 6 and Fig; 7 of the drawings is as efiicient as the arrangement previously disclosed on Fig. 3 and Fig. 4 of the drawings, whenuse is made of the same type of equipment.

The static disturbances received and internal disturbances originating in the equipments preceding the band filters of Fig. 6, are transmitted to terminals I5, l6l!, l8l9,' 20 and 2], 22 through filters H1, 2, J1 and J2 in four distinct waves a V (a) Through filter Hi to terminals |5 |s -mNaC'4 cos (pz+p+pn) t+ a'} 7 I the'element G of the drawingsis wired to common bus-bars cc to The negative sign is used in view of the position T1.

(12) Through filter Hz to terminals |1|8 Through filter J1 to terminals Ill- -mNcC'4 COS {(pl-l-pn) t-l-gtc'} The negative sign is used in view of the transposition T2 inserted between element G and the -input circuit offilter J1.

(d) Through filter J2 and terminals 2 I, 22

+mNaC4 cos {(p1+pn) t+ d} The term 12 in all of the above expressions is equal to 21r f.

After transmission through elements K1 and Li of Fig. 7, and bearing in mind the transposition trans T3 between terminals 23, 24 and 25, 26, the expression for the Wave 4: becomes +mNaC'4C cos (pnt-lm") Similarly, Wave b may be written as given by-- -m'NbC4C 00S (fini-l-(pbf') The corresponding expressions for Waves 0 and d will be given by The above expression can be readily reduced to the following equivalent form, which gives the final value of the static disturbances:

In the above formula the given by As previously discussed, there appears to be, no factual evidence to show that, while 909.", cpb", (pc" and god" may take any values, their differences will not be zero, or practically equal to zero. Under these conditions we evidently can write-- tinuous function of frequency and that, further, if the ratio of the frequency width of the signal values of N and X are spectrum to the carrier frequency is sufliciently small, then the following relations can be assumed as maximum probable for the range of frequencies included in the medium frequency broadcasting range:

The ratio r of the noise power, with the radio transmitting and receiving system as just described to the Noise. power which would have been obtained with the standard double side band system of the present art, when the last system is;operating' at a carrier frequency of f1+f) cycles, is given-by-- The above ratio corresponds to a relative reduction of static disturbances equal to, in decibels- I r=l0log10 =40 decibels The ratio of signal tofnoise power is also proved by the same 40 db., since the signal power of the. system. above disclosed is equal to that ofthedouble side band system of the present art.- 1 1 The system just described can be still further improved by the use of 2 channels for speech transmission with 2 channels for noise reception, where n takes the values 1, 2, a, 4, etc. The equipment costs increase quite rapidly with n,,the separation of carrier assignments becomes greater; decreasing thereby the number of available broadcasting stations. Even with the arrangement of Fig. 6 and Fig. 7 of the drawings,

-th'ereceiving equipment is quite costly, since four duplicate systems of modulators, amplifiers, oscillators, etc., are required. Of course, the improvement indicated of 40 db. may not be required and the simple system first described, shown on Fig. 1, Fig. 2,. Fig. 3 and Fig. 4 may prove amply sufficient. There are, however, other radio applications of signal transmission, such as television,'wherein the more complex arrangements indicated above may prove invaluable.

In many cases it will be possible to improve the performance of the systems previously described hereinabove by the installation of an adjustable artificial pad P and phase changer Q of the lattice type, as shown on Fig. 8 of the drawings.

Considering the simplest case firstthat of the single side band system of Fig, 5, Fig. 2, Fig. 3 andFig. 4 of the drawings, we will assume that, with the transmitting carrier set at (f2+f0) cycles, the filters H and J of Fig. 3 of the drawings are designed with the following cutoff points:

Higher Lower Filter V FilterJ' -l fz fz f m'zvoid'z as; (put-PX) where-- s x Neale-2mm cos b'- i')1v and Na-.9Nb as a probable maximum as previously discussed, the" installation of the artificial pad P would make it possible to completely balance Na and Nb as to amplitude,-wh ile phase changer Q would eliminate. any small difference (e an) that may be existing. The pad required would be a l-db. pad, aslso-called in the art, and would reduce the amplitude Nb by about 10%. Hence the new value Nb =0.90Nb'=N. On the face of it, this neutralization would completely eliminate static and there would be no reason for any of the more complicated balancing schemes heretofore indicated. This would be the case if the origins or sources of disturbance remained fixed in space as well as in amplitude.

To secure complete neutralization with the pad scheme, it would be necessary to have it adjustable and to adjust it more or less continuously, either manually or automatically. The adjustment of the pad P for relative amplitude and that of'Q for relative phase will not influence the signal reception since no signals will be flowing through the special equipment or, Fig. 8 of the drawings. This, is a tremendous advantage.

In the case of the double side band transmission system of the present specifications, the amplitude adjustment has no detrimental effect since the pad P is formed of non-inductive resistances and afiects all frequencies alike. The phase adjustment, however, may have to berestricted to definitely small limits of variation with frequency.

All of the systems/so far described utilize a band frequency equal in width to that of the signal spectrum or some multiple thereof. It is also possible to secure equivalent efiects in static reduction by subdividing or chopping-up the signal spectrum at the transmitting end, recombining these subdivided sections with their proper phase relations at the receiving end so as not to afiect the reception of signalsin any way, I

but neutralizing the static disturbances. In general, the signal spectrum will be dividedinto 2" parts, where n is some integer. The subdivision will therefore be carried out into 2, 4, 8, etc., parts, depending upon the value given to the numeric n. The order not to complicate unduly the drawings and the description of the system, we will assume n=l. Thus the signal spectrum is divided into just two equalparts. For the same assumption just made, the equipment arrangements required to carry out the purposes of the invention will be givenby'Fig. 1, Fig. 2, Fig. 3 and Fig- 4 ofthe drawings, but the design features will be'somewhat different from those'previouslyfollowed, as. indicated below. The supply ofcarriers C1 and' C2 on Fig, 1 of the drawings will be made at the frequencies of f1 and v (fl-Pg) Cutoff frequencies Higher Lower f Band pass filter A 11+) Band pass filter B fl+g T1 The signal modulated .by

carrier C2 at a frequency of V I r I v (fll') I cycles per second will have the usual two side bands. The lower side band will be eliminated by filter A. The upper side band will have frequency components in the range The portion of the components having the frequency (23+)) and 7 will be passed by filterv A. This portion thus transmitted through corresponds to signal waves having the frequency range and 2 to f We will designate these vwaves by where qz represents in generic terms 211- multiwhich includes components in the frequency range (15+ The portion of those components having the frequency range will be passed through by filter B, the remaining portion being strongly attenuated or eliminated.

It would be possible, without departing fromthe spirit of the specifications, to inert filters in 7 the supply circuit of. the signal wave itself, to chop up this wave into the two portions 7 and g to) cycles There appears to be no outstanding advantage in this alternative and it has not, therefore, 7

been illustrated to avoid adding unduly to the drawings and specifications. The filters A and B are required anyway to eliminate the lower side band products of the two modulation circuits of Fig. l of the drawings.

The modulated wave reaching terminals 1, 8 will be given by the expression kC'Sz S{(Pi +g+qflt+ 9}+ IOCSA (1 1+ Q1) 9} where q1==21r x frequency of wave included in the band 0 to cycles qz=21r frequency of waves included in the band to f cycles S1=Amplitude of a component of the signal wave in the range V 0 to g cycles Sz=Amplitude of a component of the signal wave in the range g to f cycles 1 =Width of signal spectrum.

The wave given by Equation 3'7 is amplified and stepped up by the frequency f0 through the equipment shown on Figure 2 of the drawings. This stepping up of the frequency may be carried in two steps, instead of a single step as shown on the drawings, when and if so required. The wave radiated by the transmitting antenna is given by- The wave given by Equation 38 is received by the receiving antenna of Fig. 3 of the drawings, amplified by element F to the extent desired and carried through the intermediate frequency demodulation step, using element G of the drawings. The filters H and J are designed with exactly the same cutoff points as filters A and B, respectively. Under the conditions indicated, the waves reaching terminals l5-I6 and l1-l8 of the drawings will be given by The positive sign of Wave 39 is due to the transposition l3, l4-l5, l6.

Wave 39 is transmitted through elements K1 and L1 of Fig. 4 of the drawings, with the local carrier to element L1 supplied at a frequency cycles. Wave 40 is transmitted through elements K2 and L2 of 'Fig. 4, with the local carrier supply to element L2 at a frequency of 11 cycles per second. With the above design features in mind, it will be evident that the signal wave reaching the audio or signal equipment, after transmission through filter M will be given by The two terms, in combination, represent the entire signal spectrumoriginally supplied at the transmitting end, except for the multiplier l'CCaCiC'; We may therefore express the above in the more compact form v The low pass filterM, as previously, is designed for the free pass band 0 to f cycles.

We will designate by N the instantaneous value ofthe intensityof a component of the noise disturbances in. the frequency spectrum and by Nb the corresponding intensity of asimilar component in the frequency band The respective phase differences will be indicated by a and b. If, as heretofore, we indicate by (fo+f1+f+f1|) the frequency of the noise component Ne, and by (f0+fl+fn) that of the component Nb, then the entire noise or static disturbance efiect, as finally received in the signal or-audio equipment will be given by the summationwhere NNa 2NaNb cos t")+1vb= and to X is given by Equation 10.

tion with the above Formula 43 are 1. The summation is carried between the frequency intervals Oto 2. The absolute difference infrequency between a component (Na'fn) and Nwfn) is actually J.

In view of Point 2 just made, as previously we can assume that Na=0.90 Nb- The noise power, as so-called, which is proportional to the frequency interval included in the summation, is now given by a quantity proportional to For the double side band transmission system of the present art, the noise power is proportional to (NH-N19 or 3.61 No. Hence, the ratio of the relative noise powers is given by- (45) r (decibels) =10 log361=25.'7decibels The above improvement can be further increased by the use of the adjustable Dad P and phase changer Q of Fig. 8 of the drawings which The important points to remember in connecobtained will be no flow of modulated signal waves' through I ments of Fig. 3 and Fig.4 of thedrawings. l

7 At the'transmitting end,=using Fig.' l an'd'Figg 2 of the drawings,'the carrier oscillators-are set to the following frequencies: C2 tothe frequency and Ci to thefreqriency. f1. 1 Thecutoff points of the band pass filters are set, for band pass filter A, to e (Mi a d(f1+f) passfilter B, to V, g g nd g It-will be notedfthat this arrangement at the transmitting-end is exactlythe sameas with the case just previously described. The transmitted waveis therefore given by Equation 38, previously derived.

( .kCCaS2{ (pt+p1+-g+q2) +0} 'ccasg tts-(pt+p1+1) 'l V At the receiving .end, the filters H1, H2, J1 and J2 would be designedon the following basis as to their cutoff 'points Cutoff frequencies Higher .Lower fl+ f fl'i'af m-a-g n+1 I er. i 5+; 1 f:

The components of the first portion of Wave 38, after demodulation by element G of Fig. 6 of the drawings, are included in the frequency I I I (f1.+ )t (fr+f-)' since qz includes the components of the original signal spectrum in the range i. 2 f 1 Therefore, the first partof the transmitted Wave 38 flows 'through filte'r The second. part of this. same Wave 38 has its components in the frequencyband V V I .(fi t ft Hence, this second part of Wave 38=flows through filter J2.

It follows, as a result of'the design methods used, both at the transmitting end and at the receivingend (Fig.6 of the drawings) that there The modulated'signal waves flowing through filter. H2 will be further amplified and demodue" lated byeIements K2 and L2; Thewaves flowing throughfilterJz will be. amplified and-demodulated by elements .Kt'andln. The four toscillathe frequencies (hi-5f) (fitf), (f1+%) n fi respectively. The final signal wave will be given, under the above iassumed'conditions, by .7

The sum of the twowaves represents exactly the original'sig'nal wave, multipliedb y the numeric lCCsCtC. The change in sign of the first term of Wave 46 is due to transposition T3 of Fig. 7 of the drawings. It is. clear. at oncethat Equations 43 and 46 are identical and fromthe standthrough all four band filters of Fig. 60f the drawings. The performance of the equipment shown on Fig. 6 and Fig. 7 of the drawings will be exactly the sameas heretofore described in detail, except for the fact that the total frequency band width of the static disturbancesrec eived is one-half of that previously assumed. The final static wave received will therefore be given by the summation of Equation 32, withthe evident exception that the summation for'the variable frequency in for" the noise is carried out between V 0 and 5 A v instead of 0 and}. The intensity of individual components of the noise-Wave will be given "by Equation 34 with the following changes in the The ratio of the "noise power with the arrangement of Fig. 6 and Fig.7 of the drawings, 4 I

of the drawings was considered is given by improvement in the ra'tioof the signal to noise power, with the arrangement of Fig. 6 and F1g. 7 of the drawings; as'compared with the arrangement of Fig. 3 and Fig. 4 of the drawings, is given.by I

" r,=j1o1tgf%%i0(2.557;.1.398) Y I i r/r"=;-1 1.0 deciben 7 u 7 The total relative "improvement -with respect to the double side band arrangement of the present art 1s given by ('25.6+1-1.6),'or '3-7 111)., approximately.

aasaaee 1 3 The securing of'the above improvement, outstanding in character, is contingent, as well known to those versed in the art, upon'the accuracy'with which the various elements entering into the amplifiers, demodulators, carrier supplies, etc., can be furnished. It is essential, also, that the carrier supplies, both at the transmitting and receiving ends, be obtained with the same phase. This will require the use of harmonic generation of frequencies. Such a system is described in B. S. Technical Journal October 1937, page 437. Any deficiencies in the above respects can be remedied, at least in part, through the use of the neutralizing equipment of Fig. 8 of the drawings. When the receiving equipment is wired in accordance with Fig. 6 and Fig. 7 of the drawings, it will prove of advantage-one neutralizing equipment of the type shown on Fig. 8 of the drawings between demodulator L2 and terminals 23, 24, and a second neutralizing equipment of the same type between demodulator L4 and terminals 21, 28. 1 A third neutralizing equipment, for still finer adjustment, would be wired between terminals 21, 28 and low pass filter M.

Since the adjustments required would be less 1 db. in any case, it is not believed the fidelity of reproduction of the signal will be appreciably affected. If the adjustments made for the neutralizing equipment between L2 and terminals 23, 24 on one hand and those made in conjunction with the similar equipment between demodulator L4 and terminals 21, 28 on the other hand are made equal to each other, part of the relatively minor difficulty just referred to would be eliminated. The neutralizing equipment adjustments can be used, as pointed out above, to serve two different purposes. The first purpose would be to insure the theoretically perfect performance of the circuits shown on Fig. 1, Fig. 2, Fig. 6 and Fig. '7 of the drawings. This particular purpose is achieved by fixed adjustments. The second purpose, more difficult of attainment, requires or may require continuously variable adjustments. If this second purpose is achieved, then the im-' provements obtainable go beyondthose indicated herein as practicable to obtain by the theoretically perfect performance of the circuits of Fig. 1, Fig. 2, Fig. 6 and Fig. '7 of the drawings.

A detail account was given in the preceding sections of the present specifications of the means and methods required to secure a substantial reduction in static interference, a primary objective of the present invention. The following additional advantages are inherent in the system disclosed hereinabove, though not specifically claimed. 1

1. The transmission system disclosed herein is also inherently a system of secret transmission.

2. The receiving system is extremely effective in lowering the internal noise level of the receiving set.

Referring to the first of the above points of advantage, it must be apparent immediately that the transmitted wave as given by Equation 2 cannot be received by the standard type double side band radio receiver of today.

Referring to the second point of advantage, it is a well known fact that, in the absence of static interference, whether due to natural or manmade causes, the maximum amplification possible with the receiving set is limited by the internal noise level of the receiving set. This noise, in turn, is predominantly associated with the elements of the first tube of the receiving set. Now, in the receiving set, as illustrated on Fig. 3 and Fig. 4 of the drawings, the first tube marked F is common to the two alternative paths into which the received waves are directed through elements K1 L1 and elements K2 and L2 respectively. The internal noise originating in tube F divides itself in equal proportions into the two paths and, in .view of the transposition between terminals 13, M and l5, [6 in the first path, these two portions mutually cancel each other. The noise in tube F of Fig. 3 of the drawings is given by the expression, in terms of the mean square voltage For an understanding of the notation used, see "Fluctuation noise in vacuum tubes, Bell System Technical Journal, October 1934, page 643. As brought out in said paper the noise power due to thermal agitation in the grid and plate circuits is distributed equally over all frequencies. It is this last feature and the further point that there exists no difference in attentuation asbetween the different frequencies of the noise spectrum, in a band 10,000 cycles wide, between the point of origin of the predominant noise (i. e. tube F) and the final audio receiver, that make it possible to eliminate the internal noise more effectively than the static interference.

I-claim:

, 1. In a radio transmitting system, means for modulating the same signal at two different carrier frequencies, means for selecting the upper side bands of the respective modulation products in each case, means for reversing the phase of only one of said side bands, and means for radiating both the reversed and the unreversed side bands.

2-. In a radio transmitting system, means for modulating the same signal at two different carrier frequencies, means for selecting the lower side bands of the respective modulation products in each case, means for reversing the phase of only one of said side bands, and means for radiating both the reversed and the unreversed side bands.

3. In a radio transmitting system, means for modulating the same signal at 2 different carrier frequencies where n is an integer, means for selecting the 2 upper side bands of the respective modulation products, said side bands constitutinga sequence of frequencies of increasing magnitude, means for reversing the phase of every alternate side band, and means for radiating all said upper side bands. 4. In a radio transmitting system, means for modulating the same signal at 2 different carrier frequencies where n is an integer, means for selecting the 2 lower side bands of the respective modulation products, said side bands constituting a sequence of frequencies of increasing magnitude, means for reversing the phase of every alternate side band, and means for radiating all said lower side bands.

5. In a radio transmitting system, means for subdividing the original signal spectrum into 2 parts, where n is some integer, means for modulating each such part separately by a different carrier, means for selecting the 2 upper side bands of the respective modulation products, said side bands constituting a sequence of frequencies of increasing magnitude, means for reversing the phase of every alternate side band, and means for radiating all said upper side bands.

6. In a radio transmitting system, means for subdividing the original signal spectrum into 2 parts where n is some integer, means for modulating each such partseparately bya oliiferent carrier, 'means for selectingthe 2 lower side bands ofthe respectivemodulationproducts, said side bands constituting asequ'ence of frequencies of increasing magnitude, means for reversing the phase of every alternate side band, andmeans for radiating all said lower side bands. I

"7. a radio system arranged for single side band receiving, means for separating all incorn meansfor retaining only the lower side band in each channel, and means for-reversing the phase of one of the side bands, producing thereby two,

distinct static waves in phase opposition.

8, In a radio, receiving-system, the method of reducing static and internal noise which con'' sists in segregating such noise and the received signal impulses into two frequency bands sep-' arated by. the width of the originalsignalspec trum, introducing a phase reversal intorone' of said'frequency bands, translating said disturbances into two exactly similar disturbance waves but opposite in phase, covering the same frequency interval, and means for recombining into a single wave, with proper phase relationship, the signal impulses'received insaid two frequency b s. a

9. In a radio receiving system arranged for static andinternal disturbance reduction, means for separating incoming waves into twodifferent frequency-channels, a separate carrier supply in each channel, means for separately demodulating the received waves with carriersupplied to each channel, means for retaining only thelowerv side bands of the demodulation products in each channel, and means for reversing the'phase 'of only one of the side bands, thereby" producing two; distinct disturbance-waves in phase oppo sition. 7 i '10. A radio receiving system comprisingan antenna, a radio frequency amplifier, an intermediate frequency detector, a source of intermediate frequency carrier supply associated with said detector, band pass filters for segregating the detected waveslinto two frequency channels, a source of carrier supply in each frequency channel, means for detecting in each saidjchan; nel with aforesaid carriersupply, means for retaining only the lower side bands, of the demodulation products in each channel, means for reversing the phase only of one of said side bands, a common low pass filter and signal responsive means. l

11. In a system for the radio transmission of signals, the method of reducing static and in-.

I ternal disturbances at the receiving end which consists in segregating said disturbances into four frequency bands, translating said disturbances into four similar waves, each covering the same fre'quency band'butwith the second wave oppos ing the first, and theifourth wave opposing the amazes 12; m a system for the radio transmission ofthe received wavesin each said channel, .means for retaining only the lower side bands of the demodulation products, andmeans for revers ing the phase of only one of'the side bands in" cooperative relation with the I transmitting sys-= tem s'pecifie'd in claim 1 for restoring the signal impulses in the two channels in proper phase relationship impulse. a

13. In a system for the radio transmission of f signals, a radio receiving circuit for the trails mitting system specified in claim 2 comprising means for separating incoming waves into two different frequency channels, a separate carrier" supply'in each channel, means for demodulating? the receivedwaves in each said channel, means for retaining only the lower side bands of the demodulation products, and means for reversing the phase of only one of the side bands in 00- operative relation with the transmitting system specified in-claim 2 for restoring the signal-fin pulses in the two channels-in proper phase relationship into a single reinforced signal impulse;

'14. In a system for the radio transmission of signals, a receiving circuit for the transmitting system specified in claim 3 comprising means for separating incoming waves into 2 consecutively numbered different frequency channels, where n is some integer, a carrier supply in each such channeL- means for demodulating the received Waves by carrier supplied in each channel, means for selecting'the lower side bands in each such demodulated wave, means for reversing alter nately and in sequence the phase of said side bands, means for recombining all odd numbered side bands into asingle channel and all even numbered side bands into another channel, means for reversing the phaseof one of said channels and means for recombining both channels in cooperative relation with the transmitting system,

specified in claim 3 for restricting the signal im-;

signals, a receiving circuit forthe transmittingv system specified in' claim 4 comprising means for third, combiningthe first and second waves into signal impulses into thesecond and fourth of said frequency band si l separating incoming waves into 2 consecutively numbered different frequency'channels, where-u is some integer, 'a carrier supply in each such channel, means for demodulating the received waves by carrier supplied in each channel, means for selecting the lower side bands in each such demodulated wave, means for reversing-alternately and in sequence the phase of said side bands, means for recombining all odd numbered side bands into a single channel and all-even numbered side hands into another channel, means for reversing the phase of one of said channels and means for recombining both-chanc nels in cooperative relation with the transmitting system specified in claim 4' for restricting the signal impulses to theeven: numbered channels. l

into a single reinforced signal combination with means for radiating both of said retained side bands.

17. In a radio transmitting circuit comprising means for modulating the same signal by two carriers separated in frequency by the width of the signal spectrum, means for selecting the upper side bands of the modulation products, means for suppressing both carriers and the lower side bands, means for reversing the phase of only one of the retained side bands in combination with means for radiating both of said retained side bands.

18. In a radio transmitting circuit comprising means for modulating the same signal by two carriers adjacent in frequency, means for selecting the lower side bands of the modulation products, means for suppressing both carriers and the upper side bands, means for reversing the phase of only one of the retained side bands in combination with means for radiating both of said retained side bands.

19. In a radio transmitting circuit comprising means for modulating the same signal by two carriers separated in frequency by the width of the signal spectrum, means for selecting the lower side bands of the modulation products, means for suppressing both carriers and the upper side bands, means for reversing the phase of only one of the retained side bands in combination with means for radiating both of said retained side bands.

20. In a radio transmitting system, means for modulating the same signal at 2 different carrier frequencies where n is some integer, means for selecting the upper side bands of the respective modulation products, means for reversing alternately and in sequence the phase of said side bands, means for combining adjacent channels by sub-groups of two into 2 channels, means for reversing alternately and in sequence the phase of said 2- channels, means for repeating the procedure of phase reversal and proressive reduction in number of channels until all 2 channels are reduced in number to a single final channel and means for radiating all side bands of the upper type in said final channel.

21. In a radio transmitting system, means for modulating the same signal at 2 different carrier frequencies where n is some integer, means for selecting the lower side bands of the respec- 22. In a system for the transmission of radio signals, a radio receiving circuit comprising means for separating incoming waves into 2 different frequency channels where n is some integer, a separate carrier supply in each channel, means for demodulating the received waves in each channel, means for selecting the lower side bands of each such demodulated wave, means for reversing alternately and in sequence the.

phase of said side bands, means for combining adjacent channels by sub-groups of two into 2 channels, means for repeating the procedure of phase reversal and progressive reduction in number of channels until all 2 channels are reduced in number to a single final channel in cooperative relation with the transmitting system of claim 20 as to the phase reversals of the dinerent frequency channels for reinforcing the signal impulses received.

' 23. In a system for the transmission of radio signals, a radio receiving circuit comprising means for separating incoming waves into 2 difierent frequency channels where n is some integer, a separate carrier supply in each channel, means for demodulating the received waves in each channel, means for selecting the lower side bands of each such demodulated wave, means for reversing alternately and in sequence the phase of said side bands, means for combining adjacent channels by sub-groups of two into 2 channels, means for repeating the procedure of phase reversal and progressive reduction in number of channels until all 2 channels are reduced in number to a single final channel in cooperative relation with the transmitting system of claim 21 as to the phase reversals of the different frequency channels for reinforcing the signal impulses received.

HUGHES MOURADIAN. 

